vrwm: Fix startup flickering

Sometimes starting an app appears similar to a 2D app or a VR app +
window. This changes the logic to avoid that.

If a dim or extra layer appears after the 2D app layers then consider
it to be hidden

Bug: 35915107
Test: start permissionsgen several times
Change-Id: If66d1b06cc6c688c26b856e9b5aeee9d1b8940f7